Showing papers by "Jet Propulsion Laboratory published in 1991"
TL;DR: Investigations of more rapid fluctuations bear on meteorological studies of interannual, seasonal, and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations.
Abstract: Recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth's rotation. The interpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth-moon system and dynamical processes in the liquid metallic core of the earth (where the geomagnetic field originates), other parts of the earth's interior, and the hydrosphere and atmosphere. Fluctuations in the length of the day occurring on decadal time scales have implications for the topographay of the core-mantle boundary and the electrical, magnetic, ande other properties of the core and lower mantle. Investigations of more rapid fluctuations bear on meteorological studies of interannual, seasonal, and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations.
349 citations
TL;DR: In this article, the authors found an emission-line galaxy at a redshift of 2.286, and with the enormous far-infrared luminosity of 3 × 10^(14) times that of the Sun.
Abstract: DURING a survey intended to measure redshifts for 1,400 galaxies identified with faint sources detected by the Infrared Astronomy Satellite, we found an emission-line galaxy at a redshift of 2.286, and with the enormous far-infrared luminosity of 3 × 10^(14) times that of the Sun (L_☉). The spectrum is very unusual, showing lines of high excitation but with very weak Lyman-α emission. A self-absorbed synchrotron model for the infrared energy distribution cannot be ruled out, but a thermal origin seems more plausible. A radio-quiet quasar embedded in a very dusty galaxy could account for the infrared emission, as might a starburst embedded in 1−10 × 10^9 M_☉ of dust. The latter case demands so much dust that the object would probably be a massive galaxy in the process of formation. In either case, this is a remarkable object, and the presence of a large amount of dust in an object of such high redshift implies the generation of heavy elements at an early cosmological epoch.
216 citations
TL;DR: In this article, the authors derived diameters of 1.2, 1.0, and 3.4 km for the earth-approaching asteroids 1983 RD, 1980 PA, and 1985 DO2, whose spectra are virtually identical to that of the basaltic-surfaced large asteroid, Vesta.
129 citations
01 Sep 1991
TL;DR: The Berlekamp-Massey iterative algorithm for decoding BCH codes is modified to eliminate the calculation of inverses, which is useful in the practical application of multiple-error-correcting BCH or RS codes.
Abstract: The Berlekamp-Massey iterative algorithm for decoding BCH codes is modified to eliminate the calculation of inverses. This new algorithm is useful in the practical application of multiple-error-correcting BCH or RS codes. A VLSI architecture is developed for this algorithm.<
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129 citations
TL;DR: A one-dimensional model calculation shows that this mechanism can account for the enrichment in 18O in the stratospheric CO2 observed by Gamo et al.
Abstract: We propose a novel mechanism for isotopic exchange between CO_2 and O_3 via O(^1D) + CO_2 → CO_3^* followed by CO_3^* → CO_2 + O(^3P). A one-dimensional model calculation shows that this mechanism can account for the enrichment in ^(18)O in the stratospheric CO_2 observed by Gamo et al. [1989], using the heavy O_3 profile observed by Mauersberger [1981]. The implications of this mechanism for other stratospheric species and as a source of isotopically heavy CO_2 in the troposphere are briefly discussed.
125 citations
TL;DR: Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus and reveals a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth.
Abstract: Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 Km^3/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.
118 citations
TL;DR: The steps by which the telemetry data were converted into spectra suitable for analysis, the analysis software and methods developed for the atmospheric and solar studies, and the ATMOS data analysis facility are described.
Abstract: The atmospheric trace molecule spectroscopy (ATMOS) instrument, a high-speed Fourier transform spectrometer operating in the middle IR (2.2-16 microns), recorded more than 1500 solar spectra at about 0.0105/cm resolution during its first mission onboard the shuttle Challenger in the spring of 1985. These spectra were acquired during high-sun conditions for studies of the solar atmosphere and during low-sun conditions for studies of the earth's upper atmosphere. This paper describes the steps by which the telemetry data were converted into spectra suitable for analysis, the analysis software and methods developed for the atmospheric and solar studies, and the ATMOS data analysis facility.
116 citations
TL;DR: In this article, the authors used the ATMOS Fourier transform spectrometer to detect CO lines of high rotational excitation energy and have never been observed before in the laboratory.
114 citations
Cornell University1, Ames Research Center2, California Institute of Technology3, Jet Propulsion Laboratory4, United States Geological Survey5, Science Applications International Corporation6, RAND Corporation7, Arizona State University8, University of Arizona9, Brown University10, NASA Headquarters11
TL;DR: Images of Venus taken at 418 (violet) and 986 (NIR) nanometers show that the morphology and motions of large-scale features change with depth in the cloud deck, and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation ofLarge-scale planetary waves.
Abstract: Images of Venus taken at 418 (violet) and 986 [near-infrared (NIR)] nanometers show that the morphology and motions of large-scale features change with depth in the cloud deck. Poleward meridional velocities, seen in both spectral regions, are much reduced in the NIR In the south polar region the markings in the two wavelength bands are strongly anticorrelated. The images follow the changing state of the upper cloud layer downwind of the subsolar point, and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large-scale planetary waves. No optical lightning was detected.
99 citations
TL;DR: In this article, the occurrence of the 22-micron overtone of C triple-bond N's stretching fundamental mode in all four classes of small solar system bodies is suggested to serve as a diagnostic of both exposure duration and degree of modification of surface materials.
98 citations
TL;DR: The Chicxulub crater is the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe as mentioned in this paper, and it is argued that the origin of the cenote ring is related to post-impact subsidence of the crater rim.
Abstract: Research throughout the Caribbean suggests that the geophysical anomalies in the Yucatan first noted by Penfield and Camargo (1981) and called the Chicxulub crater could be the site of the impact purported to have caused the K/T extinctions. A semicircular ring of sink holes, known locally as cenotes, which correlates with the geophysical anomalies has been identified, and it is argued that the origin of the cenote ring is related to postimpact subsidence of the Chicxulub crater rim. If there is indeed a crater, the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km. If confirmed as a site of impact, the Chicxulub crater would be the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe.
TL;DR: In this article, the lateral modes of an ideal broad area laser, including the nonlinear interaction between the carriers and the optical field, were calculated and the results showed that unsaturable losses are higher and quantum efficiencies are lower than those determined from plane-wave approximations.
Abstract: Calculations of the lateral modes of an ideal broad area laser, including the nonlinear interaction between the carriers and the optical field, are made. The results include periodically modulated near fields and single- and double-lobed far fields similar to those previously measured. The unsaturable losses are higher and quantum efficiencies are lower than those determined from plane-wave approximations. Broad area InGaAs-GaAlAs-GaAs quantum-well lasers were fabricated and measured and found to closely agree with the theory in near, far, and spectrally resolved near fields. An occultation experiment on the far field confirms previously predicted unstable resonatorlike modes with V-shaped fronts. >
TL;DR: During the Galileo flyby of Venus the plasma wave instrument was used to search for impulsive radio signals from lightning and to investigate locally generated plasma waves, which have considerable fine structure because of the formation of soliton-like wave packets.
Abstract: During the Galileo flyby of Venus the plasma wave instrument was used to search for impulsive radio signals from lightning and to investigate locally generated plasma waves. A total of nine events were detected in the frequency range from 100 kilohertz to 5.6 megahertz. Although the signals are weak, lightning is the only known source of these signals. Near the bow shock two types of locally generated plasma waves were observed, low-frequency electromagnetic waves from about 5 to 50 hertz and electron plasma oscillation at about 45 kilohertz. The plasma oscillations have considerable fine structure, possibly because of the formation of soliton-like wave packets.
01 Jul 1991
TL;DR: In this paper, an approximate correlation between experimental results and a prediction of proton-induced displacement damage is presented, and possible explanations for remaining inconsistencies are discussed, and it is now possible to predict the effect of complicated space proton environments upon CCD charge transfer efficiency and other CCD performance parameters.
Abstract: Recent analytical and experimental work has provided new insights into the production of damage sites in silicon Charge-Coupled Devices (CCDs) by energetic particles and into the effects of these sites on CCD performance. An approximate correlation is presented between experimental results and a prediction of proton-induced displacement damage, and possible explanations for remaining inconsistencies are discussed. As a consequence of this agreement, it is now possible to predict the effect of complicated space proton environments upon CCD charge transfer efficiency and other CCD performance parameters. This prediction requires evaluation of the damage resulting from only a small number (
01 Dec 1991
TL;DR: The application of aperture synthesis concepts, used for many years in radioastronomy to achieve high image resolution at a reasonable cost, to remote sensing technology is discussed in this article.
Abstract: The application of aperture synthesis concepts, used for many years in radioastronomy to achieve high image resolution at a reasonable cost, to remote sensing technology is discussed. The electronically scanned thinned array radiometer (ESTAR) is put forward as a viable alternative to improve spatial resolution by an order of magnitude over what is presently achieved by microwave imaging systems that are collecting data from Earth orbit. Future developments in airborne sensor technology and potential spacecraft application are described. >
TL;DR: Initial Magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes, ejecta deposits extending up to 1000 kilometers to the west of several impact craters, windblown deposits and features in areas where there are both obstacles and a source of particulate material.
Abstract: Initial Magellan observations reveal a planet with high dielectric constant materials exposed preferentially in elevated regions with high slopes, ejecta deposits extending up to 1000 kilometers to the west of several impact craters, windblown deposits and features in areas where there are both obstacles and a source of particulate material, and evidence for slow, steady degradation by atmosphere-surface interactions and mass movements.
TL;DR: Neutral sodium emissions encircling Jupiter exhibit an intricate and variable structure that is well matched by a simple loss process from Io's atmosphere, implying that fast neutral sodium is created locally in the Io plasma torus, both near Io and as much as 8 hours downstream.
Abstract: Neutral sodium emissions encircling Jupiter exhibit an intricate and variable structure that is well matched by a simple loss process from Io's atmosphere. These observations imply that fast neutral sodium is created locally in the Io plasma torus, both near Io and as much as 8 hours downstream. Sodium-bearing molecules may be present in Io's upper atmosphere, where they are ionized by the plasma torus and swept downstream. The molecular ions dissociate and dissociatively recombine on a short time scale, releasing neutral fragments into escape trajectories from Jupiter. This theory explains a diverse set of sodium observations, and it implies that molecular reactions (particularly electron impact ionization and dissociation) are important at the top of Io's atmosphere.
09 Jul 1991
TL;DR: This paper concentrates on the importance of 'information bottlenecks,' which restrict the amount of information that can be handled at different stages of analysis in the primate visual system.
Abstract: In its evolution, the primate visual system has developed impressive capabilities for recognizing complex patterns in natural images. This process involves many stages of analysis and a variety of information processing strategies. This paper concentrates on the importance of 'information bottlenecks,' which restrict the amount of information that can be handled at different stages of analysis. These steps are crucial for reducing the overwhelming computational complexity associated with recognizing countless objects from arbitrary viewing angles, distances, and perspectives. The process of directed visual attention is an especially important information bottleneck because of its flexibility in determining how information is routed to high-level pattern recognition centers.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: Atomic force microscopy and x-ray diffractometry were used to study 1500-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 substrate and showed large regions that correspond to a face-centered cubic surface and distortions of this surface.
Abstract: Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.
01 Aug 1991
TL;DR: In this paper, the authors used the Langley-Bouguer technique to calibrate four solar radiometers on days with a clear, stable atmosphere, achieving an uncertainty of less than six percent, corresponding to a maximum uncertainty of 0.06 in optical depth.
Abstract: Calibrated solar radiometer intercepts allow spectral optical depths to be determined for days with intermittently clear skies. This is of particular importance on satellite sensor calibration days that are cloudy except at the time of image acquisition. This paper describes the calibration of four solar radiometers using the Langley-Bouguer technique for data collected on days with a clear, stable atmosphere. Intercepts are determined with an uncertainty of less than six percent, corresponding to a maximum uncertainty of 0.06 in optical depth. The spread of voltage intercepts calculated in this process is carried through three methods of radiometric calibration of satellite sensors to yield an uncertainty in radiance at the top of the atmosphere of less than one percent associated with the uncertainty in solar radiometer intercepts for a range of ground reflectances.
24 Jun 1991
TL;DR: Initial results indicate that there are significant variations in the surface scattering function, and this relation suggests that a phase change or differences in chemical weathering occur at about 6055-kilometer radius.
Abstract: Magellan probes Venus' surface by 12.6-cm-wavelength vertical and oblique radar scattering and measures microwave thermal emission. Emissivity and root-meansquare slope maps between 330° and 30°E and 90°N and 80°S are dissimilar, although some local features are exceptions. Inferred surface emissivities typically are ∼0.85, but vary from ∼0.35 at Maxwell to ∼0.95 northeast of Gula Mons and other locations. Lowest emissivities appear in topographically high areas; this relation suggests that a phase change or differences in chemical weathering occur at about 6055-kilometer radius. Initial results indicate that there are significant variations in the surface scattering function.
TL;DR: A bound is derived and analyzed for the bit error rate (BER) of a Viterbi decoder with survivor truncation and estimates of the SNR loss on the AWGN channel due to truncation are obtained for convolutional codes.
Abstract: A bound is derived and analyzed for the bit error rate (BER) of a Viterbi decoder with survivor truncation. Estimates of the SNR (signal-to-noise ratio) loss on the AWGN (additive white Gaussian noise) channel due to truncation are obtained for convolutional codes. Larger truncation lengths are required than the smallest value that does not effectively decrease the code's free distance, especially at low E/sub b//N/sub 0/. >
01 Apr 1991
TL;DR: The presence of formantlike resonances in cat vocalizations and the important role of jaw movements (vocal gestures) in the production of these calls suggest that cats may provide a useful model for some aspects of human vocal behavior.
Abstract: Feline isolation calls were analyzed, and a model was developed to relate the acoustical features of these calls to the physical processes used in their production. Fifty isolation calls were recorded from each of five cats for a total sample of 250 vocalizations. By combinations of Fourier transform, autocorrelation, and linear prediction methods, the fundamental frequency (glottal‐pulse period) F0, the energy of F0, the frequency having maximum energy Fmax (not always F0), and the energy at this frequency were computed. Mean F0 ranged from 400–600 Hz for individual cats. For some cats F0 was consistent within calls, but for other cats sudden shifts in F0 occurred within calls. Here, Fmax was almost always a harmonic of F0 and generally ranged from 1–2 kHz. For individual cats, the energy ratio E = (energy of Fmax/energy of F0) varied from 1 to 60 and the grand average E over the time course of the call varied from about 12 to 38. The mean rms call intensity was an inverted‐U function of time. Measured jaw opening was strongly correlated with acoustical features of call. A Bessel‐horn model with time‐varying flare gave a good account of acoustical parameters such as Fmax. The presence of formantlike resonances in cat vocalizations and the important role of jaw movements (vocal gestures) in the production of these calls suggest that cats may provide a useful model for some aspects of human vocal behavior.
TL;DR: In this article, a lidar facility has been established at the Jet Propulsion Laboratory-Table Mountain Facility located at an altitude of 2300 m in the San Gabriel Mountains in Southern California.
Abstract: A lidar facility has been established at the Jet Propulsion Laboratory-Table Mountain Facility located at an altitude of 2300 m in the San Gabriel Mountains in Southern California. This facility is using the technique of differential absorption lidar to measure atmospheric ozone concentration profiles. Two separate systems are needed to obtain the profile from the ground up to an altitude of 45 to 50 km. An Nd:YAG-based system is described for measurements from the ground up to 15 to 20 km altitude, and an excimer-laser-based system for measurements from 15 km to 45 to 50 km altitude. The systems were designed to make high-precision, long-term measurements to aid in the detection of changes in the atmospheric ozone abundance through participation in the Network of Detection of Stratospheric Change.
01 Feb 1991
TL;DR: High fidelity computer graphics preview and predictive displays provide substantial aid in four major space telerobotic activities: overall workspace design including viewing conditions specific workspace analysis for given tasks in a fixed setting operator training and reduction of operator''s uncertainty and operation time under communication time delay conditions.
Abstract: The application of computer graphics in space telerobotics research and development work is briefly reviewed and illustrated by specific examples implemented in real time operation. The applications are discussed under the following four major categories: preview displays, predictive displays, sensor data displays, and control system status displays.
TL;DR: A Tropospheric Emission Spectrometer for the Earth Observing System (EOS) series of polar-orbiting platforms is described, aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere.
Abstract: A Tropospheric Emission Spectrometer (TES) for the Earth Observing System (EOS) series of polar-orbiting platforms is described. TES is aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere, urban and regional pollution, acid rain precursors, sources and sinks of greenhouse gases, and the interchange of gases between the troposphere and the stratosphere. TES is a high-resolution (0.025/cm) infrared Fourier transform spectrometer operating in the passive thermal-emission mode in a very wide spectral range (600 to 4350/cm; 2.3 to 16.7 microns). TES has 32 spatial pixels in each of four optically conjugated linear detector arrays, each optimized for a different spectral region.
TL;DR: In this paper, techniques for enhancing the accuracy of the geophysical data records derived from Geosat altimeter observations with treatments for water-vapor correction and satellite orbit were described.
Abstract: Techniques are described for enhancing the accuracy of the geophysical data records derived from Geosat altimeter observations with treatments for water-vapor correction and satellite orbit. The TOVS/Special Sensor Microwave Imager (SSMI) water vapor data and T2 ephemeris are used to effectively adjust tide-gauge records. The T2 orbit is found to be effective for the study of large-scale phenomena with reductions in the radial orbit error.
Proceedings Article•
14 Jul 1991TL;DR: This paper describes a system which processes local sensor data in such a way as to allow efficient, reactive local navigation, and experiments with this system, both in simulation, and with a real robot operating in natural terrain.
Abstract: In order to navigate autonomously, most robot systems are provided with some sort of global terrain map. To make storage practical, these maps usually have a high-level symbolic representation of the terrain. The robot's symbolic map is then used to plan a local path. This paper describes a system which uses the reverse (and perhaps more natural) process. This system processes local sensor data in such a way as to allow efficient, reactive local navigation. A byproduct of this navigation process is an abstraction of the terrain information which forms a global symbolic terrain map of the terrain through which the robot has passed. Since this map is in the same format as that used by the local navigation system, the map is easy for the system to use, augment, or correct. Compared with the data from which the maps are created, the maps are very space efficient, and can be modified, or used for navigation in real-time. Experiments with this system, both in simulation, and with a real robot operating in natural terrain, are described.